We describe quantum wires and point contacts fabricated in GaAs/AlxGa1−xAs heterostructures that are free of the disorder introduced by modulation doping and in which the electron density and the confining potential are separately adjustable by lithographically defined gates. We observe conductance plateaus quantized near even multiples of e2/h in 2 μm wires and up to 15 conductance steps in 5 μm wires at temperatures below 1 K. Near the conductance threshold the quantum point contact and the 2 μm wire both show additional structure below 2e2/h.

Zero length quantum wires (or point contacts) exhibit unexplained conductance structure close to 0.7 × 2e 2 /h in the absence of an applied magnetic field. We have studied the density-and temperature-dependent conductance of ultra-low-disorder GaAs/AlGaAs quantum wires with nominal lengths l=0 and 2µm, fabricated from structures free of the disorder associated with modulation doping. In a direct comparison we observe structure near 0.7 × 2e 2 /h for l=0 whereas the l = 2µm wires show structure evolving with increasing electron density to 0.5 × 2e 2 /h in zero magnetic field, the value expected for an ideal spin-split sub-band. Our results suggest the dominant mechanism through which electrons interact can be strongly affected by the length of the 1D region.73.61.-r, 73.23.Ad, 73.61.Ey III-V

No abstract

We report developing coplanar waveguide devices which can perform dielectric spectroscopy on biological samples within a microfluidic channel or well. Since coupling to the fluid sample is capacitive, no surface functionalization or chemical sample preparation are required. Data on cell suspensions and solutions of proteins and nucleic acids spanning the frequency range from 40 Hz to 26.5 GHz are presented. Low-frequency data are well explained using a simple dispersion model. At microwave frequencies, the devices yield reproducible and distinguishable spectral responses for hemoglobin solution and live E. coli.